FAMILIAL CORTICAL MYOCLONIC TREMOR AS A UNIQUE FORM OF CORTICAL REFLEX MYOCLONUS

Previously it was reported that some patients with tremor had the same electrophysiological findings as those seen in patients with cortical reflex myoclonus, and consequently the tremor was named ''cortical tr emor.'' In the present study, we examined six patients from three fami lies with cortical tremor of relatively late onset. The inheritance pa ttern of cortical tremor was compatible with autosomal dominant trait. Those patients had relatively rhythmic involuntary movements (tremor) in the distal upper and lower limbs, especially during posture and/or fine movements. There: was no cerebellar ataxia or dementia, and fits of loss of consciousness occurred only infrequently. Electrophysiolog ically, they had generalized spikes on electroencephalogram (EEG), gia nt cortical components of somatosensory evoked potential, an enhanced long-loop reflex (C-reflex), and cortical spikes preceding the rhythmi c jerk demonstrable by the jerk-locked back averaging method, thus ful filling the criteria of cortical reflex myoclonus. Furthermore, they h ad normal slow negative EEG shift starting 1-2 s prior to voluntary mo vements, suggesting that, as opposed to the conventional form of progr essive myoclonus epilepsy (PME), the cerebellar efferent input to the motor cortices was normal. These clinical and electrophysiological pic tures are distinct from those of familial essential tremor, familial e ssential myoclonus, or the conventional form of PME, and the term ''fa milial cortical myoclonic tremor'' will represent the clinical and ele ctrophysiological features of this unique entity most appropriately.